Damage only on one side of the plant or one area of the room

Likely causes, most likely first

Ranked for this sign on its own. Your stage, medium and readings change the order, so run the checker for your plant.

1. LikelyWind burn from a fan blowing directly on leaves

   EnvironmentLow urgencyRead: Airflow: air exchange, canopy air speed and fan placement

   Fix: Aim fans across and under the canopy, not straight at leaves: leaves should rustle, not thrash (roughly 0.3-1.0 m/s at leaf level). Damaged leaves stay damaged. Cannabis-specific evidence is grower observation.

   Recovery: No new damage on the fan side within a week.

   How to confirm it

   • Compare with siblings or the same cut. Put the affected plant beside siblings or clones of the same cut in the same conditions. A trait shared by all of a cultivar (purple stems, foxtailing, pale colour) is genetic; a problem on one plant points to its roots, a virus or its genetics; a problem on every cultivar points to the environment or feed.

2. Less likelyPhysical damage (kinks, splits, broken branches)

   Physical damageDeal with it this weekRead: HST and supercropping: controlled stem crushing

   Fix: Splint and tape a split stem within hours (tape, plant tie or a straw splint); a supercropped knuckle heals stronger in 3-7 days. Remove fully broken branches with a clean cut. Support heavy colas with a trellis.

   Recovery: Leaves above the wound regain turgor within 1-2 days; a callus forms within a week.

   How to confirm it

   • Cut a wilting stem lengthwise. On a wilting or dying branch, scrape the lower stem and cut it lengthwise with a clean blade. Brown streaks in the water-conducting tissue point to vascular wilt (Fusarium). A dark, sunken crown points to crown rot. Disinfect the blade afterwards.

3. Less likelyFusarium wilt or crown rot

   DiseaseAct within a day or twoRead: Fusarium in cannabis: wilt, crown rot and bud rot

   Fix: No cure once infected: remove the plant with its medium in a bag, sanitise pots, trays and water lines, and use clean clones and new media. Reduce root stress (overwatering, heat, salts) on the rest.

   Recovery: No further wilting plants over the next 2-3 weeks.

   How to confirm it

   • Cut a wilting stem lengthwise. On a wilting or dying branch, scrape the lower stem and cut it lengthwise with a clean blade. Brown streaks in the water-conducting tissue point to vascular wilt (Fusarium). A dark, sunken crown points to crown rot. Disinfect the blade afterwards.
   • Send a sample to a plant diagnostic lab. For rots, wilts, leaf spots and viruses you can't separate by eye, send a fresh sample (whole plant with roots or a wilting branch with healthy and diseased tissue) in a sealed bag to a university or commercial plant diagnostic clinic. Results in days to 2 weeks.
   • Look at the roots. Hydro: lift the net pot and look at the root mass in good white light. Containers: tip the plant out with a hand over the medium and look at the edges and bottom of the root ball. Healthy roots are white to cream with fine fuzzy tips. Brown roots whose outer layer slides off between the fingers leave a bare thread: rot. Firm, evenly tan roots with white tips in coloured solution are staining.

4. Less likelyHerbicide drift or residue

   Physical damageDeal with it this weekRead: Why are my cannabis leaves curling? The master curling and clawing decision tree

   Fix: Outdoors or with contaminated compost, manure or straw (persistent herbicide residues). Remove the source, repot into clean media; new growth may normalise slowly. Cannabis-specific symptom descriptions are scarce.

   Recovery: New growth normalises over 2-4 weeks after the source is removed.

   How to confirm it

   • Magnifier check of leaf undersides and new growth. Use a 10-20x loupe for spider mites, thrips, aphids and whiteflies, and a 30-60x lens or clip-on phone macro for broad and russet mites. Check the undersides of 10 affected leaves across several plants and the newest shoot tips, in white light. Look for moving dots, eggs, shed skins, webbing, slender insects with black specks, and glassy specks on new growth.
   • Send a sample to a plant diagnostic lab. For rots, wilts, leaf spots and viruses you can't separate by eye, send a fresh sample (whole plant with roots or a wilting branch with healthy and diseased tissue) in a sealed bag to a university or commercial plant diagnostic clinic. Results in days to 2 weeks.

Look for

Wide shot of the space showing where the damaged plants or branches sit relative to fans, lamp and vents..